The hundreds of reporters and camera operators who crowded into the Brooklyn megachurch two summers ago had come to see one woman: Nafissatou Diallo, the hotel housekeeper who was accusing the head of the International Monetary Fund, Dominique Strauss-Kahn, of sexually assaulting her.

But it was Ms. Diallo’s lawyer, Kenneth P. Thompson, who had orchestrated the setting and the spotlight, echoing other racially charged cases in the city’s past.

“We take a stand for every woman around the world who has been raped or sexually assaulted and has been too afraid to speak out,” he announced in a grave baritone.

In more than one way, it was the climax of Mr. Thompson’s career. Standing in the Christian Cultural Center, the politically influential church with a predominantly black congregation whose pastor had nurtured him and whose congregants had brought him clients and connections, he was flanked by politicians to whom he had been close for years as he introduced the client who had made him famous as far away as France.

To political veterans, it also looked like the beginning of a campaign. And now, Mr. Thompson, 47, who is said to have aspired to elected office for years, is making the first run of his life, challenging the vulnerable Brooklyn district attorney, Charles J. Hynes, a 23-year incumbent.

Largely unknown even in legal circles until he became Ms. Diallo’s lawyer, Mr. Thompson embarked that summer on a publicity campaign intended, he said, to restore dignity and justice to Ms. Diallo. But to critics of the way he represented Ms. Diallo, Mr. Thompson only hastened the case’s collapse, alienating prosecutors while his star rose.

“He certainly seemed to be courting publicity to him for its own sake, and not because it served any strategic goal in the case,” said Jane Manning, a vice president at the National Organization for Women and former sex crimes prosecutor who worked with other women’s rights advocates on Ms. Diallo’s behalf. By antagonizing prosecutors, she said, “He was single-handedly making it impossible that D.S.K. would ever be brought to justice.”

Still, even a few detractors conceded that he seemed genuinely passionate about giving a voice to a poor African immigrant accusing the man who could have been France’s president.

Introducing himself in the campaign as a civil rights lawyer, Mr. Thompson characterizes his representation of Ms. Diallo as the culmination of a career spent standing up for victims.

“Ms. Diallo was being vilified to the world, being called a liar,” he said in an interview. “I was not going to stand on the sidelines while Ms. Diallo was being portrayed that way. But I was able to get her some justice.” (Though charges against Mr. Strauss-Kahn were dropped, Ms. Diallo won an undisclosed settlement in a lawsuit.)

Mr. Thompson’s other clients have included several women who sued for employment discrimination and victims of the 2007 Midtown steam pipe explosion; his Fifth Avenue firm, Thompson Wigdor, has also represented executives at investment banks, hedge funds and other companies sued for discrimination. His prosperity has meant a comfortable life in Clinton Hill, where he lives in a brownstone with his wife, Lu-Shawn, a nurse, and two young children.

But Mr. Thompson has never been content with a quiet, if highly successful, private practice, friends said.

A reserved man who wears wool suits even in the height of summer, Kenneth Paul Thompson grew up in Co-op City in the Bronx, where he was raised by a single mother, among the first female police officers to patrol the streets.

At New York University Law School, he could seem out of place — for years, he wore a pair of glasses taped in the middle — but he was already pursuing lofty dreams of public service.

Photo

Mr. Thompson, a successful lawyer mounting his first campaign, is challenging the vulnerable Brooklyn district attorney, Charles J. Hynes.Credit
Michael Nagle for The New York Times

A professor, Ron Noble, gave Mr. Thompson his first job, at the Treasury Department, where Mr. Noble, now the head of Interpol, was leading a review of the Branch Davidian raid in Waco, Tex., that ended in a fire and more than 80 deaths in 1993.

He became a federal prosecutor in Brooklyn, but his early time in the courts was marked by rookie mistakes, like showing up late or neglecting his case preparations. Judge Sterling Johnson Jr., to whom Mr. Thompson often turned for advice, recalled the time Mr. Thompson walked into his courtroom after a lunch break, biting blithely into a large doughnut. Judge Johnson, who preaches punctuality and courtroom decorum, was not amused. “He had a lot of talent, but he was a project,” Judge Johnson said.

A few years into his time as a federal prosecutor, Mr. Thompson was assigned to a case that became a critical moment for him: that of Abner Louima, who was beaten and sodomized by police officers in 1997, becoming a national symbol of police brutality. A courtroom sketch of Mr. Thompson giving the opening statement, which others hailed as eloquent and powerful, has pride of place over his desk in his law firm office. His law firm biography of nearly 1,300 words notes that the columnist Jimmy Breslin called his performance one “that will be remembered.”

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He said he loved litigation, and decided to run only after a health scare last summer, when he was hospitalized for a blood clot.

But some lawyers who have worked with or against Mr. Thompson said they believed that his political ambition dated from further back. He originally moved to Brooklyn partly because he believed he had a better chance of getting elected in Brooklyn than in the Bronx, where he grew up, said Anthony L. Ricco, a longtime friend, in a 2011 interview. His primary motivation, Mr. Ricco said, was to “make a difference, to see that justice is done.”

But the Rev. A. R. Bernard, his pastor at the Christian Cultural Center for nearly 20 years, advised him to build a stable career and family before he jumped into politics.

So he did: soon after the Louima case, he moved to Morgan, Lewis & Bockius, a large firm. He and two others then left to found their own firm. Meanwhile, Mr. Thompson built longstanding relationships with several African-American politicians of his generation, including State Senator John L. Sampson and Hakeem Jeffries, a Brooklyn congressman who has endorsed him. Both stood by Mr. Thompson during the 2011 news conference.

Mr. Thompson has donated to a Sampson campaign, and represented him when the State Senate Democrats, which Mr. Sampson led, were fighting a subpoena in the investigation into the Aqueduct racetrack casino deal. But Mr. Sampson, who was indicted this year on embezzlement and other charges, has stayed away from Mr. Thompson’s race as Mr. Hynes’s campaign questioned the connection.

Though he had no formal role in the courtroom during the Strauss-Kahn prosecution, Mr. Thompson carved out a position rallying public opinion.

Before the charges were dismissed, signs emerged that Mr. Strauss-Kahn’s lawyers planned to argue that the sexual encounter was consensual. Prosecutors began to doubt Ms. Diallo’s account because of inconsistencies in her interviews with them about her own background, including a story she fabricated about having been gang-raped in Guinea. As the case appeared to crumble amid concerns about Ms. Diallo’s credibility, Mr. Thompson graphically detailed evidence of what she claimed was assault, accused the Manhattan district attorney, Cyrus R. Vance Jr., of leaking damaging information about her, and called for a special prosecutor to replace Mr. Vance, who declined to speak about Mr. Thompson.

For all his insistence that Mr. Vance pursue the charges, Mr. Thompson was seen as a destructive force by prosecutors and women’s rights advocates. His relationship with prosecutors soured as he blocked them from meeting with her for 19 days, frustrating any attempts to rebuild the case.

And he allowed Ms. Diallo to reveal her identity, which had previously been withheld by American news organizations, in interviews with Newsweek and “Good Morning America.” Other lawyers were aghast, given that Mr. Strauss-Kahn’s lawyers could erode her credibility by picking apart inconsistencies between her news media interviews and her courtroom testimony. Ultimately, prosecutors dropped the case.

But Mr. Thompson’s defenders countered that in an atmosphere where Ms. Diallo had been called a prostitute by The New York Post, he had to represent her as aggressively as possible.

“This is a case of things being prosecuted in the public media,” Mr. Noble said. “He had to make her whole in the court of public opinion.”

Mr. Thompson did not shield himself from the cameras, either: “You could see a person who had been a supporting actor becoming a lead actor in an Academy Award-winning film,” Mr. Noble said.

Mr. Thompson announced his candidacy the next year, 2012. One of Mr. Strauss-Kahn’s lawyers has donated $1,000.

A version of this article appears in print on August 21, 2013, on Page A17 of the New York edition with the headline: Candidate for Brooklyn Prosecutor Drew Criticism for Case That Made His Name. Order Reprints|Today's Paper|Subscribe